Conventionally, a water treatment method was carried out to remove suspended matter from various types of service water and draining water by added a flocculant to the water to cause flocculation and precipitation of the suspended matter. Polyacrylamide, aluminum sulfate, and the like have been used as flocculants for water treatment.
Such flocculants require pH adjustment during water treatment, and there are concerns not only about the complications in water treatment that arise, but about the safety of the water after treatment. Further, there was the problem that adequate flocculation effects are not obtained with aluminum sulfate when the temperature of the water to be processed is low.
A variety of flocculants comprising a silicon-colloidal solution in which silicon is dissolved are known that are non-toxic and safe and have high flocculation effects that can solve these problems (refer to Patent Literature 1 to 4).
(Patent Literature 1) Unexamined Patent Application Number 20003-38908 (Japan).
(Patent Literature 2) Patent Number 2759853 (Japan).
(Patent Literature 3) Patent Number 2732067 (Japan).
(Patent Literature 4) Published Examined Patent Application H4-75796 (Japan).
With a silicon colloidal solution, however, it is difficult to maintain a stable solution state for a long time; sodium silicate (H4SiO4), a general silicon solution, needs to be made alkaline and stabilized in a solution state with an electric potential. In order to make a silicon colloidal solution into a strong acid or strongly alkaline and maintain a solution state as with the flocculants mentioned in Patent Literature 1 to 4, there are the problems that concerns arise regarding the pH value of the water after processing, and that gelation due to neutralization of the silicon colloidal solution is inadequate, so the pH of the water needs to be adjusted.